This invention relates in general to roller-type rock bits and more particularly to a rock bit in which the cutters revolve on tapered roller bearings.
Oil and gas wells as well as large water supply wells and other deep holes in soft, medium, and even hard rock formations are drilled with roller-type rock bits. The typical bit of this nature has a body with three legs projected downwardly from it, and each leg has an inwardly directed spindle about which a cone-shaped cutter revolves. The cutter has teeth on its exterior and, when used, is subjected to both radial and thrust loads. As a consequence both radial and thrust bearings exist between each cutter and the spindle about which it revolves.
The body of the bit attaches to the end of a drill rod, and as that shaft rotates the cutters bear against the rock and produce a drill hole. Actually the cutters roll against the bottom of the drill hole and in effect chisel, crush, chip and otherwise gnaw away at the rock formation so as to make the hole deeper. For a roller-type rock bit to operate effectively, its cutters must bear against the rock with considerable force. At shallow depths this force is derived from hydraulic cylinders which urge the drill rod downwardly. At greater depths the weight of the drill rod itself supplies the necessary force. In either case the force is substantial, and this, coupled with the severe environmental conditions that are encountered, causes the bearings by which the cutters are mounted on their respective spindles to fail, often long before the cutters themselves wear out.
In conventional roller-type rock bits, the cone-shaped cutters are mounted on their respective spindles by a combination of cylindrical roller bearings, ball bearings, and plain thrust bearings. The cylindrical roller bearing takes radial loading only, while the plain thrust bearing takes only thrust or axial loading. The ball bearing, on the other hand, is configured to take both radial and thrust loading, but the balls of this bearing, support loads only at points along their raceways. As a consequence, severe stresses develop along these raceways. Also, at the plain thrust bearing high friction develops at the mating surfaces of the bearing. Consequently most failures occur in the ball and plain thrust bearing. Once the bearings of a conventional roller-type bit fail the bit is discarded for it is practically impossible to disassemble the bit for replacement of the bearings.
A single tapered roller bearing has the capacity for taking both radial and thrust loads. Heretofore attempts have been made to mount the cone-shaped cutters on their spindles with tapered roller bearings and thereby take advantage of this capacity, but these attempts have been generally unsuccessful, resulting in mountings that were overly complex or else difficult to keep free of rock cuttings. U.S. Pat. Nos. 3,193,028 and 3,847,235 illustrate such mountings.